A cushion-pressure controller which can restrict surge pressure at the start of press molding and pressure override at a switching of press driving speed has been proposed in Japanese Laid-Open Patent Application No. 5-131295 (“JP '295”).
The cushion pressure controller of the die-cushion device adjusts an opening degree of a servo valve provided in a discharge flow passage of a hydraulic cylinder by an operation amount signal generated based on a control deviation between a predetermined cushion pressure value and a hydraulic detected value of the hydraulic cylinder supporting a cushion pad and the operation amount signal is additionally changed according to a driving speed of a press slide.
Also, a die-cushion device provided with an NC servo valve for obtaining a cushion action through pressure control of a cushion cylinder of the cushion pad and a position control servo valve for carrying out preliminary acceleration, auxiliary lift, locking and elevating of the cushion pad by control of pressure oil to be supplied to/discharged from an upper chamber and a lower chamber of the hydraulic cylinder supporting the die cushion pad is proposed in Japanese Laid-Open Patent Application No. 7-24600 (“JP '600”).